Radio receiving system



Feb. 19, 1924; 1,484,411

H. S. READ RADIO RECEIVING SYSTEM Filed Sept 14, 1920 -/nvenfor:

. Harry S.f? ead. y Aff Patented Feb. 19, 1924.

UNITED STATES,

PATENT OFFICE."

HARRY S. READ, OF ITHACA, NEW YORK, ASSIGNOR T0 WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK. N. Y., A CORPORATION OF NEW YORK.

RADIO RECEIVING SYSTEM.

Application filed September 14, 1920. Serial No. 410,235:

To all whom it may concern:

Be it known that I, HARRY S. READ, a citizen of the United States, residing at Ithaca, in the county. of Tompkins, State of New York, have invented certain new and useful Improvements in Radio Receivin Systems, of which the following is a ful, clear, concise, and exact description.

This invention relates to a circuitarrangement for interlinking three or more circuits in such a manner as to provide a particular functional relationship therebetween, and its principal object is to prevent mutual feeding of power or exchange of energy between two of the circuits but to permit the two cir-' cuits to feed independent of each other into the other circuits.

The invention has for its object the provision of means to maintain a relationshipof associated circuits such that two of the circuits are independently related to a third circuit or other circuit-s into which they feed but between which two circuits no interaction can exist.

It is a further object of the invention to provide a connection of amplifier or antenna,

a local oscillation generator, and a detector,.

in a heterodyne receiving system which will permit the first and second circuits to feed into a detector circuit but which will prevent the two circuits from feeding into each other.

Further objects of the invention will appear as the specific details thereof are disclosed in the description that follows.

As illustrating an application of the invention, which will be hereinafter described in greater detail, the circuit arrangement may be used to interconnect the three circuits of a heterodyne receivingsystem in which a high frequency wave is received by an antenna circuit and combined with a locally generated wave of slightly different circuits of the invention which has uni-' lateral conductivity will, to some extent at least, avoid these undesirable effects. An

amplifier inserted between the antenna and detector circuits might be efi'ectivefor this purpose but on account of the effective capacity in the tube circuits, the amplifier is not a unilateral transmission circuit and at high frequencies an undesirable amount of energy can pass backwards through an amplifier' lation according to well known principles.

In addition to the function of the circuits of the invention, as stated above, to prevent radiation of the focally generated wave, the additional function is accomplished of preventing undesirable modulation. voltage derived from the local source is im-. pressed on the output circuit of the amplifier, or amplifiers, .it may cause some energy to feed back through one or more of the amplifier units. Whether or not there is an actual feed back, there will be a modulation of two frequencies which are present. This will result in the presence in the input of the detecting device of a complex wave containing componentsmade up of the sum of frequencies concerned and other frequencies,

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differing from the input components which tually prevents intermodulation before detection of the received, and local frequencies. The invention in one aspect resides in'the use of a closed impedance circuit of a con- C ventional four-arni'Wheatstone bridge, to

junction points of which three circuits are connected, the output (in the particular application chosen, a detector circuit) being connected across one arm or a portion of an arm, and the other. two circuits bein opposite junction points. If the bridge is balanced in the usual manner, there is a zero con-1 nected respectively to alternative pairs of diflerence of potential between the points at which each of the input circuits are connected, when a difference of potential is from either input circuit. Forthe purpose of the detailed description and claims following, a Wheatstone bridge may be defined broadly as a closed impedance circuit in which the impedance elements are of such relative values and so arranged that there are two pairs of points, between the points of each of which there is a zero difference in potential when a difference in otential is impressed between the points 0 the other pair. It is immaterial, for the purposes of definition, whether the differences of po tential are impressed inductively or conductively. and, accordingly, the definition includes within its terms various types of balances networks or hybrid coil circuits.

As further illustrating the invention, reference is made to the following detailed description, with its'accompanying drawings, in which Fig. 1 is an enlarged view of the zircuit arrangements of the invention without reference to the particular types of circuits with which it is adapted to be used and Fig. 2 is a circuit diagram of a preferred system in which the invention may be used.

Referring to Fig. l, the closed circuit which includes 'the four impedances Z Z Z and Z is suggestive of the closed impedance'circuit of a simple type of Wheatstone bridge in which the impedances here replace the resistances usually shown in the type of Wheatstone bridge used for comparative measurements of resistance. The four arms of the bridgeare here shown as impedances to indicate that pure resistances, inductances or capacities, or combinations of the above may be'used, provided only that the fundamental condition is observed, which is common to all types of four arm 7 bridges, whether constituted of resistances,

inductances or capacities, that is Z,/Z

If a difference of potential is impressed across 'Z Z, for example, by means of circuit C, there will be zero dlfi'erenceof potential between the junction points Z Z and Z Z between which points circuit A is connected. The practical significance of this is that when a potential is impressed on the bridge from circuit C,.ener from this circuit cannot feed into circuit A. Conversely when a potential is impressed on the bridge from circuit A, the energy from this circuit cannot flo'w in circuit G. Since c1rcu1t B is associated with a slngle arm of the bridge and since current flows in this arm, when a difference of potential of either polarity is impressed on the bridge by either of circuits A and C, there will necessarily be a diiference of. potential between the points across which this circuit is connected. Accordingly either circuit C orcircuit A, each independently of the other, may feed into circuit B, or both circuits may feed simultaneously into circuit B, superposing their separate effects in this circuit.

In applications of the inventive idea hereinafter to be disclosed in specific circuit systems, the-circuit B will be designated as the output circuit and the circuits A and C as input circuits. 'It is immaterial as to the polarity of the respective input terminals,

immaterial whether the. elements composing circuit, energy from each being transmit-ted through the bridge to common circuit B.v

The energy from the source received at the bridge through circuit C, will be largely de creased on account of absorption of energy between said source and bridge. It is desirable in this case, in which the difference of potential impressed on the bridge by circuit C is small, to transmit the energy through .the bridge with as small a loss as possible. This may be accomplished by making Z and Z great as compared with Z and Z respectively This means that the output circuit is fed from the arm across which the greatest drop of potential occurs. In this case the current through Z, when a potential is impressed on the bridge by'circuit A, is less than with any other arrangement. of impedances, and hence the, energy from circuit A istransmitted less efliciently into the output circuit. In other words, increase in efliciency of transmission from circuit C is obtained at the expense of eflicient transmission from circuit A. This is pcrmissible since we are greatly concerned with efficiency from circuit C tooutput, but, since ance of the bridge.

parallel circuits comprising this arm willpedance of the fourth arm of the bridge and is included in the value of impedances Z in the equation indicating the condition of bal- The impedance of the substantially determine the impedance to be chosen for the other arms in accordance with the preceding analysis. In order that energy from circuit C may feed efficiently into circuit B and with a minimum of loss in the bridge, the bridge portion of impedance Z, should be much larger than impedance of circuit B. The impedance of circuit B would ordinarily be of the order of magnitude of at least- 600 ohms, and with this value it has been found to be desirable and convenient to make the bridge portion of impedance Z about 6000 ohms. Z would accordingly have a value between these quantities, assuming for convenience that Z,=Z. and Z =Z,. With these compara-' 'tively great impedance values, especially in the case where these uantities are made variable in order to ba ance the bridge, it is preferable to make the larger impedance elements of the bridge pure resistances. Impedances Z and Z are relatively small and fixed in value and may well be condensers since with the high frequencies used in this bridge comparatively small capacity .is required. The quality of small fixed con-.

densers, by reason of which their impedance constants vary only slightly with change in frequency and with use as compared with inductances and resistances, commends them for use'in the present arrangement.

Referring now to Fig. 2 there is here disclosed the use of a circuit arrangement of,

the invention, in what may be termed the preferred embodiment, although other uses are contemplated, and the invention should not therefore be construed as in any sense restricted to' this embodiment.

Thereis disclosed a heterodyne receiving system, the system, except as varied by the use of this invention, being old in the art.

In this system high fre uency waves from r the antenna D are ampli ed by vacuum tube E in the conventional manner, the filaments and plate ofwhich are connected into the circuit C of the bridge arrangement 1*, the circuits of which are shown the same as in Fig. 1. The circuit C-inay be connected directly to the antenna without the interposition of, the amplifier circuit if the received energy is sufficient to actuate the detector.

Input circuit. A is connected with the heterodyne oscillator G .through coupled circuits J. The oscillator functions as a generator of high frequency oscillations, the frequency of which is determined by the .adjustment of the inductance and capacity of its tuned circuit.

In the system shown the oscillator is adjusted to oscillate with a frequency slightly different from the frequency of received signal waves. These two sets of waves of different frequencies are impressed simultaneously uponthe detector H to give a beat frequency current in the telephone receiving circuit 1. In the system shown, the brid e. circuit arrangement functions as descri-be with reference to Fig. 1, to prevent interference between the amplifier and oscillator circuits but to permit each to feed independentlyinto the detector circuit. In Fig. 2 the impedances of the bridge are shown as made up of two condensers and two resistances, for the reason that has been pointed out, although the system would be operative and the theory of operation would apply equally well if the impedances were chosen otherwise, as has also been ointed out.

has been described as a heterodyne receiving system, the oscillator G may well be made to generate frequencies identical with the amplifier frequency. The system used in this way has practical application in radio telephony as may be seen by a reading of British Patent 102,503. The system disclosed in the present application is capable of use in the manner described in this patent and such use is to be understood as comprised within the scope of this invention.

Although in the example given, an alternating E. M. F. of high frequency is impressed on the bridge arrangement the 'invention should not be understood to be so limited, the theory of operation not being inconsistent with the use of any type of current whatever in the input circuit. Although the circuit B has been disclosed as connected across one arm of the bridge, it...

maybe connected between any two points between which thereis a-difi'erence of potential as, for example, across a portion of one arm or across unequal fractions of any two of the'impedances' in series, although the latter arrangement would obviously be in.- efficient. The invention should not be considered as limited to the use of a single output circuit, since as many output circuits may be used simultaneously, as there are points between which'difference of potential exists. Still further, the circuit B may be inductively instead of conductively coupled with the bridge.

What is claimed is:

1. A circuit system comprising in combination, an input circuit, a second input circuit, an output circuit, and a circuit coupllng said input crcuits to said output circuit to enable them to impress electromotive 1 Alt ough the system disclosed in Fig. 2

60 v in claim 7 inwhich'the'first-mentioned circircuit, a second input circuit, an output circuit, and a mesh circuit coupling said input and output circuits, the input circuits being connected at conjugate pairs of points in said mesh and the output circuit being connected at a pair of pointsin said mesh which are non-conjugate with respect to either of said other pairs of points.

3. In a circuit arrangement for radio receiving systems, a receiver circuit, a local oscillation circuit, a detector circuit and a mesh circuit couplingsaid circuits, the retial from said second input circuit between two points of said impedance circuit which are balanced with respect to the other-two points, an output'circuit, and means for im- "pressing on said out-putcircuit a potential derived from a third pair of points in said impedance circuit at least one point of which is different from the points in the other two pairs.

5. An anti-feed-back circuit comprising in combination, two impedance branches connected in parallel each branch consisting of two impedance elements, the ratio of the two impedances in one branch being made equal to the ratio of the similarly positioned impedances in the other branch, a circuit connected between the terminals of the impedance branches a second circuit connected between the junction points of the impedance elements in the respective branches, anda third circuit connected between the terminalg of anyone .of the impedance elements.

6. An anti-feedback circuit as disclosed inclaim 5 in which two of theimpedances as disclosed in claim .6 in which the relatively large impedances are non-inductive resistances and the other impedances are condensers; Y

8. An anti-feedback circuit as disclosed eeann I of a radio receiving system, the second-mentioned circuit is connected with a local source i of high frequency oscillations, and the third circuit is connected with a detector circuit.

9. A receiving system comprising in com bination. a receiving conductor, an assymmetrically conducting means in energy transfer relation thereto, a detector circuit, a local source of high frequency oscillations and an anti-feed-back circuit associated with the above mentioned elements, said anti-feed circuit comprising two impedance branches connected in parallel, each branch consisting of two impedance elements, the ratio of the two impedances in one branch being made equal to the ratio of the similarly positioned impedances in the other branch, the assymmetrically conducting device being connected between the terminals of the impedance branches, the local source.

being'connected between the junction points of" the impedance elements in the respectiie branches and the detector circuit being connected between the terminals of any one of" with, *a detector circuit, a .local source of high frequency oscillationsand" an antifeed-back circuit associated with the above mentioned elements, said anti-feed-back circuit comprising two, impedance branches connected in parallel, each branch consist- 1 ing of two impedance elements, the ratio of the two impedances, in one branch being made equal to the ratio of the similarly .positioned impedances in the other branch, the

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thermionic conducting device being connected between the terminals of the impedance branches, the local source beingconnected between the junction points of the impedance elements in the respective branches and the detector circuit being connected between the terminals of any one of the im edance elements.

' 11. bination, an input circuit, a second input circuit, an output circuit, and a Wheatstone bridge circuit coupling the input circuits whereby interchange of energy in either direction between said circuits is prevented,

said output circuit being connected to the.

bridge at points unbalanced with respect to each of said input circuits.

In witness; whereof, I hereunto subscribe my name this 10 day of September, A. '11, 1920.

I HARRY s. READ.

circuit system comprising in com-* 

